The growing availability of TV broadcast and interactive services creates a need for a new type of a TV control system that would facilitate user access to options offered by TV program providers. For example, direct broadcast satellite services require users to make their selection among about a thousand TV channels with various TV programs and services. Direct television satellite broadcasting is provided via direct broadcast satellites at an uplink frequency of 17.3 to 17.9 GHz and a downlink frequency of 12.2 to 12.7 Ghz.
A digital satellite television system for direct television broadcasting includes a transmitter for transmitting television signals including video and audio components to a satellite. The satellite retransmits the received television signals to an outdoor antenna assembly that includes a dish-like antenna and a block converter. The dish-like antenna directs the received television signals to the block converter that converts the frequencies of the received television signals to respective lower frequencies.
The television signals produced by the block converter are connected via a coaxial cable to an indoor satellite receiver coupled to a TV set. The satellite receiver tunes, demodulates and otherwise processes the received television signals to provide video and audio signals with a NTSC, PAL or SECAM format suitable for processing by the TV set that produces an image on a display screen in response to the video signals, and an audible response by means of speakers in response to the audio signals.
Within the transmitter, analog video and audio signals are converted to respective digital signals compressed according to the Motion Picture Expert Group (MPEG) encoding standard. The resultant digital signals are represented by a stream of packets including error correction data. The type of packets is identified by a header code. Packets corresponding to control data may also be added to the packet stream.
In the MPEG standard, the video information may be transmitted in the form of a luminance (Y) component and two color difference (U and V) components. For example, the first color difference component may represent the difference between the red image information and the luminance image information (R-Y), and the second color difference component may represent the difference between the blue image information and the luminance image information (B-Y). In addition, the color information is compressed because the two color difference components correspond to more than one picture element. The use of color difference components and the sharing of the color difference components between picture elements reduces the transmission bandwidth.
The digital information resulting from the compression and error correction encoding is modulated on a carrier using Quaternary Phase Shift Keying (QPSK) modulation and transmitted to a satellite for retransmission.
The satellite receiver comprises a tuner for selecting the appropriate carrier signal retransmitted by the satellite and for converting the frequency of the selected carrier to an intermediate frequency (IF) signal. A QPSK demodulator demodulates the IF signal and supplies it to an error-correcting decoder to correct demodulated packets representing video and audio information. An MPEG decoder decodes and decompresses video and audio packets to form digital video and audio signals supplied to a TV set. A TV set-top box serves to deliver compressed digital video and audio signals in real time usable form to one or more TV sets.
To facilitate user access to available TV programs and services, a graphical menu, such as, a list of available TV channels, may be displayed on a TV screen. To select a TV channel, a user may scan through the TV channel list using, for example, control icons displayed on the screen. Inasmuch as the digital satellite television system may provide about 1,000 TV channels, it may be hard to keep track of TV channels being scanned. Therefore, it would be desirable to provide the user with visual feedback that would indicate relative position of TV channels in the TV channel list.
Further, due to "overscan" conditions, a television receiver may produce a raster so that a picture on its screen may not be entirely in the view of the user. To prevent data loss caused by the overscan conditions, TV broadcast systems display images inside a "safe" area located within approximately a 10% border all around the edge of the screen.
In conventional TV systems, graphics data are generated so as to position graphical objects, such as control icons, inside the safe area to ensure that they appear on the screen even under the worst overscan conditions. However, such an arrangement results in reducing the size of graphical objects. This makes them difficult to find and use. The channel list is actually a sequentially ordered list. The order may be with respect to numerical channel number or alphabetical by channel name. Generally, the entire list is large and only some small subsequence of the entire list may be displayed as selectable objects on the screen. It is the location of this displayed subsequence within the full sequence that is provided as graphical feedback to the user by means of dynamically sizing the scroll bars.
Moreover, when there are no overscan conditions or overscan is less than in the worst case, a blank band leaves between the safe area and the edge of the screen.
Therefore, it would be desirable to keep graphical objects large and to fully utilize the screen area independently of overscan.